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Reverse osmosis

This is a discussion on Reverse osmosis within the Semi Hydro / Lights / Greenhouses / Accessories forums, part of the Orchid Culture category; With the shortage of untreated softer water this winter I've decided to get an RO ...

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  1. #1
    Chris in Hamilton's Avatar
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    Default Reverse osmosis

    With the shortage of untreated softer water this winter I've decided to get an RO system. I think I can have it supply our drinking water, aquarium freshening and of course the orchids. I use to use aquarium water this time of year but that was because I filled the tank with purchased distilled water. Since I started using tap I've been noticing a heavy mineral buildup. Bad enough that there are deposits at the base of most pseudo bulbs of potted plants. I use melted snow for the more sensitive but that supply is not very reliable anymore and can only be collected from a fresh fall.

    I see 6 stage systems for sale that state the water produced would have a PH level between 7.3 and 9. To me that sounds a bit high. Would a 5 stage system have a lower PH?

    Is there any real difference between 5 and 6 stage?

    I live about 1 mile from one of the largest freshwater lakes in the world but our water bill is just stupid. What kind of lost water % can I expect?

    I probably have other questions but I'm hoping the manufacturers/sellers will get back to me after the holidays and with answers without handing me a bunch of crap.

    Any help or advice much appreciated!!

  2. #2
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    Chris, I have been using-, building-, and selling RO systems for about 25 years.

    Unless the vendor in question is doing something odd, like reintroducing calcium through that last stage, the number of stages (more on that in a minute) should have little-, to no effect on the pH of the output water.

    For one, pure water is VERY difficult to get an accurate measure of its pH, due to the closely equal number of H+ and OH- charges. Secondly, pure water in a container open to the air will absorb carbon dioxide from the air, forming carbonic acid, which in today's atmosphere, will have an equilibrium pH of about 5.3.

    Stages of a basic system: Stage one is a sediment filter to remove suspended solids in the incoming water. Stage 2 is a carbon filter to remove organics. Stage three is the membrane itself, and stage 4 is a carbon "polishing" filter. If you have chlorinated water, a second carbon filter is typically added before the membrane, making the system a 5-stage.

    Unless you go with a very large, very costly system, RO systems are not "on demand" water supplies. In a typical residential system, there is typically a 3-gallon bladder tank to provide the needed water, and the system refills it as needed. Don't forget that a 100 gallon-per-day system, working at its design capacity (more to follow) is only producing about 260 ml/min, and nobody is watering anything at that rate.

    Systems are rated at 65 psi and 77F water at the membrane. Lower pressure and/or cooler temperatures lower the output.

    Standard residential systems produce 3 gallons of flush water for each gallon of pure water produced. Most of mine were on the order of 1.5 - 2:1; recently I have seen 1:1, but if your water cost is high, the extra cash for the improved membrane would be worth it. I was on a well in PA, so just dumped the wastewater on the floor of the greenhouse for humidity, but here in NC, we have very pricey water, but luckily for me, it is very low in dissolved minerals.

    If you want to know more, please email me.

  3. #3
    Chris in Hamilton's Avatar
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    Thank you Ray, I was hoping you were around. That answered a lot and might just change my mind about doing it. My incoming water is at about 60 psi but the temperature is around 45F. I'm going to see if there is some way I can reroute that flush water so its used and if there is I still might go ahead with it. I will for sure email if I have any other questions. By the by, quite enjoyed your AOS webinar talk on S/H.

  4. #4
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    If you do a search for "zero waste RO," you may find a company that has a kit that pumps that flush water into your hot water plumbing at home.

  5. #5
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    Chris, I thought you were using and storing rain water? You can also buy small water distillers but it takes about 5 hours to make a gallon.
    Posted via Mobile Device

  6. #6
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    Quote Originally Posted by sciencegal View Post
    Chris, I thought you were using and storing rain water? You can also buy small water distillers but it takes about 5 hours to make a gallon.
    Posted via Mobile Device
    I was but ran out. I've been collecting snow when we get a new fall but a 5 gallon pail tightly packed only yields a gallon of water. My greenhouse design includes a 400 gallon storage tank but that won't happen for a while I'll look into a distiller but then I'll have to consider electrical costs. Thank you!

    ---------- Post Merged at 09:47 PM ----------

    Quote Originally Posted by raybark View Post
    If you do a search for "zero waste RO," you may find a company that has a kit that pumps that flush water into your hot water plumbing at home.
    Thanks Ray, I'll do that. I wonder how that would be on the rest of the plumbing though re mineral deposits.

  7. #7
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    It's not a problem.

    The minerals rejected by an RO membrane are still in solution when flushed away, and injecting them into the hot water downstream from the water heater keeps them that way easier.

    If you get a system with a hydraulic cutoff, all water is stopped when your storage vessel is full, so it's not a constant flow anyway.

  8. #8
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    I have used RO on and off for the past 35 years. The latest systems produce far more "good" water because they use a small pump. As I understand it, RO works best with high pressure, low volume. The pump does it for the pressure . I don't know what your prices are, I understand there is a lot of import duty paid on getting the kit into UK, but my plant gives me about 150litres of water at about 12 microSiemens EC, and also leaves me with about 200 - 250 litres of "bad" water at 600 microS per day, which btw grows great dahlias in the garden - and cost about £120 pounds sterling. I took off the last cylinder which was intended to put minerals back in the water in th interests of taste , and the key thing is that when not in use it should be locked off with taps or solenoid valves so that the cylinders don't drain and dry - that increases the life many times.
    PH does not matter - yes it is quite high ( so is my feed water , so whatever is left in the water is all lime ) but it is easy to correct as rhe very last stage before using. I make up 75 litre batches of feed, and have to correct the pH every time I take anoher bucketful out of that.

  9. #9
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    I think Ray has covered it, but a few additional thoughts. Water is very dear in Germany, my water bill matches your eelctricity bill and you don't want to know about my power charges without a good dram. I've used various RO/DI units over the years, as I keep marine fish and they require purest water for mixing the salt/replacing the evaporation. I started with a standard Rowa RO 3 stage unit. Worked fine and brought my water from 900 to about 18-26!, depending on season. Wasted water, though, with a 3:1 ratio. I put the waste into my koi pond (they like it hard), so the conscience was enjoying good karma. I changed over to a Vertex Puratek Deluxe RO/DI, which had a pump, 4 stages and a 1:1 ratio. Worked a charm for over 4 years, often with a .8:1 ratio and easily 100 GPD, auto shut-off, ppm computer, ext. All the bells and whistles. Recently I started having trouble getting good membranes for it (needed one every 2 years) as cheap stuff has simply flooded the market. The cheapies cannot handle the pressure at all and clog in 4-6 WEEKS! I reconnected the 3 stage unit without pump, but added an additional restriction unit, to raise the back pressure. End of story, this improved the ratio to about 1.8:1 and the flow rate is still about 100GPD. Apparently the water pressure in my house, which is high, is enough to increase the efficiency, when given a helping hand. Now, this would not have worked when I lived in London, as the pressure was pitifull.

    Just some thoughts and, in the end, do keep it simple. Lots of units currently on the market are for 'drinking water', which means they remineralise, etc., for better taste. Pure water is truly tasteless and pH 7.0. Rainwater is tastier. Mmmm, an aemoeba.

    Jamie

  10. #10
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    Nice addition to the conversation, Geoff.

    I'll add that, in general, folks worry too much about the pH of their solutions. Yes, it should be slightly acidic for most orchids - 5.5-6.5 is a good target - but going a bit outside of that is of little, if any concern. In reality, the plant and the potting medium play a far bigger role in the in-pot pH than do the solutions applied, and that's where the pH is important.

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